The present invention generally relates to a rotary compressor and, more particularly, to a rotary compressor capable of exhibiting a relatively high working efficiency achieved by minimizing the leakage of a fluid coolant between the rotor and the end plate adjacent the rotor.
Problems associated with the coolant leakage occurring in the prior art rotary compressor used in an automobile air conditioner will first be discussed with particular reference to FIGS. 1 and 2 of the accompanying drawings which show the prior art rotary compressor of a type utilizing sliding vanes and a cross-sectional view thereof, respectively.
The rotary compressor of a type utilizing sliding vanes has come to be used in a power plant of the automobile air conditioner because of its numerous features, lightness in weight, efficiency in performance and low noise level. As shown in FIG. 1, the rotary compressor generally comprises a hollow cylinder 100 having a vane chamber 101 defined therein between a pair of opposite end plates 102 (see FIG. 2) secured to the respective ends of the cylinder 100, a rotor 103 accommodated within the cylinder 100 for eccentric rotation with respect to the longitudinal axis of the cylinder 100, and a plurality of, for example, four, vanes 105 accommodated partially in respective grooves 104, defined in the rotor 103, for movement between projected and retracted positions, each of the vanes 104 being moved to the projected position under the influence of a centrifugal force developed during the eccentric rotation of the rotor 103 with its free end held slidingly in contact with the cylinder wall defining the chamber 101.
However, when the rotary compressor of the construction described above is used in an automobile air conditioner, it has been found that the centrifugal force developed during the eccentric rotation of the rotor does not sufficiently work on each of the vanes 105 to move the latter between the projected and retracted positions smoothly. The reason therefor is that, since the rate of rotation decreases to 800 to 100 rpm when and so long as the automobile engine is operated under idling, the centrifugal force, the magnitude of which is proportional to the square of the rate of rotation, decreases to such an extent as to become insufficient to move the vanes 105.
Where each of the grooves 104 is so eccentrically formed in the rotor 103 that a respective vane of relatively great in length can be utilized, a component of the centrifugal force acting laterally of each vane 105, or a Coriolis force, acts as a frictional force to hamper a smooth movement of the respective vane 105 and, in the worst case, the tip of each of the vanes 105 may depart from the cylinder wall defining the chamber 101.
Moreover, since a pneumatic pressure inside a closed space defined between each groove 104 and the internal end of the corresponding vane 105 varies constantly according to changes in volume of the closed space and since the volume of the closed space located rearwardly of the corresponding vane 105 abruptly increases adjacent the suction port, a negative pressure is developed to restrain outward projection of the corresponding vane 105 relative to the rotor 103. Repeated movement of the vanes 105 between the projected and retracted positions without the tips held slidingly in contact with the cylinder wall, if it occurs, constitutes a major cause of noises generated by the rotary compressor.
In order to avoid the above described disadvantage, as shown in FIG. 2, a method has been employed to ensure a smooth movement of each vane between the projected and retracted positions during the eccentric rotation of the rotor 103. According to this method, the end plate 102 is formed with a substantially ring-shaped connecting groove 106 through which the spaces which are defined between the internal ends of the grooves 104 and the internal ends of the vanes 105 accommodated slidably in such grooves 104 communicate with each other, so that highly pressurized oil coupled to the discharge pressure at the discharge port can be supplied into such spaces through the connecting groove 106 as shown in FIG. 2. As shown, since the highly pressurized oil 107 acts on the internal ends of the respective vanes 105, the sliding contact of the tip of each vane 105 with the cylinder wall, which tends to be destroyed adjacent the suction area, can be ensured. However, even the construction shown in FIG. 2 involves such a disadvantage as to reduce the compression efficiency of the rotary compressor.
Specifically, since the oil 107 is pressurized by the action of a coolant, for example, furonic gas, the temperature of which has been increased by the high pressure on the discharge side, a fluid medium supplied to the connecting groove 106 is a mixture of the oil with the coolant, this mixture being supplied to the connecting groove 106 through a communicating port 108. The mixture of the oil with the coolant leaks, as shown by the arrow A in FIG. 2, from the connecting groove 106 radially outwardly into the vane chambers 101, thereby bringing about reduction in volume efficiency during low speed rotation.
In order to avoid the disadvantage inherent in the rotary compressor of the construction shown in FIG. 2, it can be contemplated to minimize the gap between the rotor 103 and the end plate adjacent the rotor, that is, minimize the gap shown by .delta. in FIG. 3, so that the resistance to the viscous flow of the leaking fluid can be increased. However, since the rotor 103, the vanes 105 and the end plate 102 are all made of either aluminum or iron material, they tend to burn easily by the effect of metal-to-metal contact which occurs as a result of thermal expansion of these component parts.
Accordingly, the maximum tolerable size of the gap according to the prior art is limited to the range of 30 to 40.mu..
When an oil of relatively high viscosity is employed, the radial leakage of the fluid medium discussed above can advantageously be minimized or substantially eliminated. Although this measure may bring about an increase of the viscous load torque between the rotor 103 and the end plate 102, an increase of the sliding resistance of the vanes 105 and the consequent increase of the volume efficiency, an adverse effect is also brought about in that the mechanical efficiency of the rotary compressor is reduced.
Although the problems evoked by the prior art rotary compressors when the latter are used in the automobile air-conditioner have been discussed, similar problems, particularly those associated with the reduced compression efficiency, equally apply even when the prior art rotary compressors are used in devices other than automobile air-conditioners. By way of example, the prior art rotary compressors, irrespective of how they are used, involve a common problem in the presence of a leakage of fluid, in a direction shown by the arrow B in FIG. 2, from one vane chamber 101 under high pressure to the next adjacent vane chamber 101 under low pressure across the rotor 103.